I don't remember from your previous post if you have any airflow going on with your grow, but if not then you need to do this. Airflow is one of the most often overlooked issues with an indoor grow. If that's in a bathroom, running the fan along with a floor fan might be a good idea. Whatever you use, air has to move in and out of the grow space for most of the day to get moisture out, which is probably causing the powder mildew and you also need to bring in CO2 from outside and moving air also helps with temperature control.